Make legend=:outertopright work

Move x to the right of the plot viewport
Perform legend size computation earlier as this computed width is required for adjusting the width of the plotarea viewport.
This adjustment has to be done before any further computations requiring this plotarea viewport width.

src/backends/gr.jl

@@ -528,7 +528,12 @@ function gr_legend_pos(s::Symbol,w,h)
         str = "topright"
     end
     if occursin("right", str)
+        if occursin("outer", str)
+            # As per https://github.com/jheinen/GR.jl/blob/master/src/jlgr.jl#L525
+            xpos = viewport_plotarea[2] + 0.11
+        else
             xpos = viewport_plotarea[2] - 0.05 - w
+        end
     elseif occursin("left", str)
         xpos = viewport_plotarea[1] + 0.11
     else
@@ -752,6 +757,43 @@ function gr_display(sp::Subplot{GRBackend}, w, h, viewport_canvas)
         end
     end
 
+    # calculate legend size
+    # has to be done now due to a potential adjustment to the plotarea given an outer legend.
+    legendn = 0
+    legendw = 0
+    legendi = 0
+    if sp[:legend] != :none
+        GR.savestate()
+        GR.selntran(0)
+        GR.setscale(0)
+        gr_set_font(legendfont(sp))
+        if sp[:legendtitle] != nothing
+            tbx, tby = gr_inqtext(0, 0, string(sp[:legendtitle]))
+            legendw = tbx[3] - tbx[1]
+            legendn += 1
+        end
+        for series in series_list(sp)
+            should_add_to_legend(series) || continue
+            legendn += 1
+            if typeof(series[:label]) <: Array
+                legendi += 1
+                lab = series[:label][i]
+            else
+                lab = series[:label]
+            end
+            tbx, tby = gr_inqtext(0, 0, string(lab))
+            legendw = max(legendw, tbx[3] - tbx[1])
+        end
+        
+        GR.setscale(1)
+        GR.selntran(1)
+        GR.restorestate()
+    end
+
+    if occursin("outer", string(sp[:legend]))
+        viewport_plotarea[2] -= legendw + 0.1
+    end
+
     # fill in the plot area background
     bg = plot_color(sp[:background_color_inside])
     gr_fill_viewport(viewport_plotarea, bg)
@@ -1313,26 +1355,9 @@ function gr_display(sp::Subplot{GRBackend}, w, h, viewport_canvas)
         GR.selntran(0)
         GR.setscale(0)
         gr_set_font(legendfont(sp))
-        w = 0
+        w = legendw
-        i = 0
+        i = legendi
-        n = 0
+        n = legendn
-        if sp[:legendtitle] != nothing
-            tbx, tby = gr_inqtext(0, 0, string(sp[:legendtitle]))
-            w = tbx[3] - tbx[1]
-            n += 1
-        end
-        for series in series_list(sp)
-            should_add_to_legend(series) || continue
-            n += 1
-            if typeof(series[:label]) <: Array
-                i += 1
-                lab = series[:label][i]
-            else
-                lab = series[:label]
-            end
-            tbx, tby = gr_inqtext(0, 0, string(lab))
-            w = max(w, tbx[3] - tbx[1])
-        end
         if w > 0
             dy = _gr_point_mult[1] * sp[:legendfontsize] * 1.75
             h = dy*n